I like the wording of the title; it emphasizes how the good things to have learned are not always the best / easiest / most pleasant things to be learning.

I view it as a matter of having enough of a background of knowledge to build an accurate mental model of the world, and to have a clue as to how to expand on it, when desired -- making future info easier to learn. Knowledge as a toolbox, basically.

For me personally, it's a big step forward every time I learn in-depth a new math concept. Same for physics; ideally, at some point, I'd like to know every physics concept relevant to engineering just about anything (if there's enough time in life for such an endeavour, of course), but that's just me and I wouldn't expect the same of other people. Other useful stuff that would aid most people... probability-aided epistemology; it helps tremendously, as most of LW could attest. A general overview of broad fields of human knowledge, and the scientific consensus on a number of important points. Enough of the life sciences to be able to recognize broad symptoms of diseases in yourself, to know what to eat and how to exercise, to have an inkling about what stuff around you is made of (chemistry), and to have an accurate view of the human organism and of the biological bases for a lot of seemingly non-biological processes. Enough history and economics to be able to discuss society and politics sanely.

I'd also add a naturalistic mindset, but according to some people (not well-represented here) that would be crossing the border into ideological impositions.

Beyond this, I think, it's a matter of specialization, intrinsic interest and curiosity, and improving job prospects.

On a tangential note, I wouldn't trust college or formal education with this task. This knowledge is much too important to allow it to be degraded into just another class to score a passing grade on. At least so I have gathered from my experience with formal education at all levels in my country; maybe things are better at the Ivies or MIT or top international universities in general, but it's a shame for society if one has to get to that percentile to have the full toolbox to think about the world around oneself. I don't think there is anything higher education institutions can do to equip people with this knowledge, and nothing short of a cultural shift to get people to read more and have a stronger appreciation for intellectual values would get the job done.